1. Field of the Invention
The present invention relates to a Wi-Fi system and, more particularly, to a method and apparatus for estimating a position of an access point (AP) in a Wi-Fi system.
2. Related Art
A widely known position measurement technique is a satellite-based system, such as a global positioning system (GPS). The GPS and similar systems employ a flying time-based range mechanism in order to accurately indicate the position of a receiver at a certain point on the earth. However, in the satellite-based system, the receiver is required to maintain the lines of sight from at least four satellites. Accordingly, the GPS is not useful in an indoor environment where most people spend time.
A variety of techniques specific to indoor environments have been developed using various kinds of signal sources, such as cell tower, TV broadcasting station, FM radio, UWB, and RFID. The specific systems require custom-made hardware and sometimes do not apply to the general public.
Recently, with the spread of Internet access based on Wi-Fi (IEEE 802.11a, b, and g standards), the number of Wi-Fi APs in urban areas is sharply increasing. This results from a smart application which requires a user to be in an on-line state anywhere. Accordingly, Wi-Fi signals for measuring positions are also actively used.
A Wi-Fi position measurement system may be divided into two kinds (that is, a coarse accuracy system and a fine accuracy system) according to the accuracy of the subject. The coarse accuracy system provides position information within a range of several tens or several hundreds of meters and suitably applies to outdoor position-based applications. The coarse accuracy system may include, for example, PlaceLab by Intel Corp. or Skyhook.
The fine accuracy system applies to indoor environments, such as shopping malls. The fine accuracy system provides position information within 10 to 20 meters from an accurate position of a target device. The fine accuracy system may include, for example, Ekahau.
One of the biggest difficulties in the Wi-Fi-based position measurement systems is a site surveying task. In the fine accuracy system, an accurate signal for a target position needs to be measured per square meters. The coarse accuracy system applies to wide areas, such as big cities, rather than specific indoor environments. Accordingly, a signal is not measured per meter. In the systems, private or public Wi-Fi is deployed in the whole city area. When the databases of APs are constructed in the whole city area, the private or public Wi-Fi matches detected APs, searches the databases for the detected APs, and estimates the positions of devices on the basis of AP position information. Next, the estimated positions are downloaded to the target devices whose positions are actually measured. Accordingly, the position of an AP becomes the most important information in such systems.
There is a need for a method and apparatus for accurately measuring the position of an AP.